The present disclosure generally relates to ambulatory infusion systems and, in particular, to venting devices for use in combination with drug cartridges and ambulatory infusion devices as well as alignment devices for aligning a drug cartridge and an adapter.
Ambulatory infusion devices that are designed to be carried by a patient during everyday life night and day for an extended time period are used in a number of therapies. Such devices especially form a basis for CSII (Continuous Subcutaneous Insulin Infusion), a therapy for diabetes mellitus.
Insulin is typically provided in a cylindrical drug cartridge. A piston is sealing received in an inner volume of the cartridge. For expelling drug out of the cartridge the piston is pushed forward from a proximal to a distal direction by a motor-driven plunger rod of the infusion device. Thereby, drug is expelled out of an outlet and into an infusion cannula. The infusion cannula is coupled to the outlet of the cartridge either directly or via intermediate fluidic components, such as tubing and, in some cases, a check-valve. The piston accordingly serves as movable wall of the cartridge such that its inner volume decreases as drug is expelled.
Since ambulatory infusion devices such as insulin pumps are carried continuously during everyday life, mechanical robustness and some degree of water protection or, preferably, full water tightness are required. Therefore, the housing is often hermetically sealed during operation and only has a sealed coupling to the infusion cannula. Because drug is expelled from the cartridge which itself is arranged inside the device housing during operation, the hermetic sealing would result, without compensation measures, in a continuous decrease of the inner pressure inside the device housing over time, potentially affecting the dosing precision. Therefore, vents typically are gas-permeable and hydrophobic membranes that may be made from Gore-Tex® or a similar material. The membrane ensures continuous pressure equalization between the inner volume of the device and the environment, while preventing water or other liquids from entering the device. In addition, the membrane ensures pressure equalization in case of varying barometric pressure, such as, for example, due to weather changes and/or changes in altitude.
In some current devices, the membrane is integral part of the device housing. A corresponding device is disclosed. This arrangement, however, has the drawback that the membrane is typically more and more clogged by dirt, fabric particles, and the like, over the device lifetime—typically in a range of some years. Thereby the pressure equalization is negatively affected and in some cases voided.
In alternative designs, the membrane is provided in a separate adapter that serves as closure for a drug cartridge compartment of the infusion device via, e.g., a skewed or bayonet connector and additionally includes a coupler for coupling an infusion tubing to the outlet of the drug cartridge. Providing the membrane in such an adapter is an improvement in so far as the adapter is typically designed for a considerably shorter lifetime as compared to the infusion device itself, thus reducing the clogging problem. This arrangement, however, has the disadvantage that it can not be used in systems that do not use a separate disposable adapter. In addition, the lifetime of the adapter may still be too long to prevent clogging.
A further specific problem arises when drug cartridges are used in an ambulatory infusion device that have an outlet which is, in the isolated state, sealing closed by a self-sealing septum. For use in the infusion system, the septum is pierced by a hollow adapter cannula that fluidic couples the inner volume of the cartridge to the infusion cannula. The adapter cannula is typically part of an adapter as described above.
FIG. 1 schematically shows a typical situation when connecting a drug cartridge with septum to an adapter. Cartridge 100 is typical cylindrical and has a proximal piston that is sealing and sliding arranged in glass or plastic body 105, cartridge body 195 having an open proximal end. At its distal end, cartridge body 105 has a constricted neck portion 110 with cap 115 that includes a central septum. Adapter 200 has an adapter body 205 from which adapter cannula 210 projects. An infusion tubing or coupler for infusion tubing is part of or connected to adapter 200 for coupling to an infusion cannula. Guide 215 is provided for positioning and aligning cartridge 100 and adapter 200. Typically, Guide 215 has the form of a collar or ring that projects from a proximal bottom surface of adapter 200 and may also carry an infusion device coupler for coupling, e.g., in form of a bayonet, for coupling to the infusion device housing. Typically, guide 215 has an axial dimension of some millimeters and surrounds, i.e., has an axial overlap with, cap 115, but not cartridge body 105.
Ideally, the cannula 210 pierces the septum perpendicular to the septum, such that the longitudinal cartridge axis Z is parallel to and preferably aligned with longitudinal cannula axis Z′. In practice, however, substantial misalignment may be typically present, as shown (somewhat exaggerated) in FIG. 1, resulting in undesired transverse forces on cannula 210 and the septum.
The possibility of significant misalignment is due to the fact that cartridge 100 is guided with respect to adapter 200 via cap 115 only which has a dimension along cartridge axis Z in a range of typically 2 mm to 3 mm, which is not sufficient to ensure axial guiding.
Consequently, the septum may leak either from beginning on or start leaking during the application time of the cartridge which is typically in a range of some days up to may be two weeks. Guide 215 typically has an inner diameter that is somewhat larger than the outer diameter of cap 115.
To improve the situation, it would, at least theoretically, be possible to design adapter 200 with a considerably extended axial length of guide 215, resulting in guide 215 to axial overlap cartridge body 105 by an amount in a range of, e.g., 7 mm to 10 mm. In addition, guide 215 would need to be provided with tight inner tolerance.
In this context, it has to be understood, however, that adapter 200 needs to meet a considerable number of partly contradictory constraints and is further regulatory critical since it is of direct significance for ensuring reliable infusion. Therefore, the development time and effort for an adapter and the corresponding interface structure of the infusion device are considerable. In practice, new adapter designs are based on existing ones as far as ever possible, with as little and preferably no modification at all to the cartridge interface. In addition, a variety of drug cartridges exists which are typically provided by different suppliers than infusion pumps and adapters. In view of the generally complex and critical adapter design, providing different adapters that ensure appropriate cartridge guiding for a variety of existing and newly developed cartridges is practically unfeasible. As a consequence, the whole ambulatory infusion system is typically designed for use with a single type of drug cartridge only.
Therefore, there is a need to provide devices that improve the situation with respect to the above-identified problems, i.e. with respect to venting and/or cartridge alignment.